Internal combustion engines typically drive several accessories through a belt arrangement powered by the engine crankshaft. Such accessories generally include an air-conditioner compressor, power steering pump and alternator, for example. A well recognized problem with conventional belt driven systems is that the accessories' rate of rotation is proportional to engine speed. The design of such accessories has thereby been compromised in order to insure adequate performance at low engine speeds and dependability and longevity at high engine speeds. To solve this problem, as well as attain other benefits including increased fuel economy, and reduced weight, noise, and vibration, it has been proposed to operate the accessories at a changeable drive ratio instead of a fixed drive ratio whereby the accessories are driven relatively faster at low engine speeds (such as idle speed) and relatively slower at high engine speeds (such as cruising speed). These various speed changing devices are mounted to the front end of the engine crankshaft and have been developed in both a continuously variable speed ratio and a discrete shift between two ratios. However, none of these prior art devices have proven to be practical from the standpoint of smoothness, space limitation, cost, or durability.
With the relatively great combined rotational inertia of the typical accessory system with power steering pump, air-conditioning compressor, and alternator, a discrete shift between a 2:1 ratio span would be of objectionable smoothness. This indicates that such an accessory drive system should shift gradually and smoothly. The converter controlled accessory drive of the present invention utilizes the speed characteristics of the automatic transmission torque converter to achieve a completely smooth ratio transition, regardless of the accessory load. The present invention also relates to a clutch controlled accessory drive wherein the accessories are driven by the clutch in a manual transmission.
The closest known transmission driven accessory drive is a PTO (power take-off). A PTO is generally a gearbox, or mechanical device used to transmit power from an engine, through a transmission, to another mechanical or hydraulic device. There are several types of PTOs, including the well established transmission-mounted model, commonly called a side mount PTO. PTO's are normally used when the vehicle is stationary, and the transmission gear which drives the PTO provides power in the amounts desired. Engine power can be of concern if operation is at low RPM and the engine is of small displacement. However, conventional PTO's do not provide two speed ratios.
Accordingly, an advantage of the present invention is the reduction of weight, noise, and vibration while increasing performance and durability of automotive accessories, thereby improving fuel economy by providing a changeable speed accessory drive driven off the transmission of a vehicle.
Another advantage of the present invention is that an accessory drive system that shifts between two speeds smoothly by utilizing the speed characteristics of an automatic transmission torque converter is provided.
Yet another advantage of the present invention is that an accessory drive system which is simple and reliable in construction and operation is attained.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.